While the prior art discloses a variety of extendable /retractable telescoping leg assemblies for tables, some of which include bearing means formed of polymeric material, the need has nevertheless remained for an assembly that is readily adjustable to provide minimal resistance to vertical sliding movement of the parts yet, at the same time, virtually eliminate play and wobble. The problem is particularly significant with large and relatively heavy tables used for drafting or reference purposes where the weight of the upper sections must be counterbalanced or where power assist is required for raising and lowering the upper sections. Under such circumstances, separation of the two sections for the purpose of adjusting the bearing elements carried by the inner telescoping members becomes a practical impossibility. If openings are provided in the outer telescoping members to permit access for adjustment purposes, such openings are not only unsightly but serve as entry points for dirt and foreign objects. The problems of achieving and maintaining smooth operation, and of adjusting the bearings to achieve such objectives, are magnified in table constructions having two (or more) telescoping pedestal legs connected to a cantilever top designed to support substantial loads, since power operation for expanding and retracting the two legs must be synchronized while at the same time both play and operating resistance must be equalized at minimum values.
U.S. Pat. Nos. 4,130,069, 3,888,444, 4,080,080, 3,004,743, 3,820,176, 2,983,474, 4,183,689, and 4,254,928 are illustrative of the known prior art.
Briefly, the adjustable leg or column assembly of this invention includes a vertical outer tube having inner surfaces defining a cavity or passage of generally rectangular cross section, a vertical inner tube telescopingly received in that cavity, the inner tube having outer surfaces of generally rectangular outline when viewed in cross section and being sufficiently smaller than the inside dimensions of the outer tube to define a perimetric space between them. A pair of vertically elongated bearing blocks of channel-shaped cross sectional configuration and of rigid polymeric material are connected to the inside of the outer tube adjacent its open end and are arranged so that the channels of the bearing blocks face each other and slidably receive opposite side portions of the rectangular inner tube. The length of the bearing blocks should be substantial (in the general range of 20 to 40% of the length of the outer telescoping tube) and at least one of the blocks should be mounted for adjustment so that its upper and lower end portions may be shifted towards and away from the contact surfaces of the inner telescoping tube. Adjustment forces, applied by adjustment screws threadedly carried by the outer telescoping tube, are distributed along the length of the adjustable block. Since the adjustment screws are readily accessible from the exterior of the outer tube, play or clearance may be easily adjusted not only at the time of manufacture or installation but also after an interval of use during which wear or loosening may have occurred. The end of the inner telescoping tube that is received in the outer tube also has bearing elements connected to it. Such bearing elements or shoes are relatively short and non-adjustable but have cross sectional configurations somewhat similar to those of the elongated bearing blocks. Also, like the bearing blocks, they are formed of rigid polymeric material.
Other features, advantages, and objects will become apparent from the specification and drawings.